#include<iostream>
#include<algorithm>
using namespace std;
unsigned long long n,a[100001],ans;
unsigned long long b[5001];
int main()
{
	cin>>n;
	for(unsigned long long i=1;i<=n;i++)
		cin>>a[i];
	sort(a+1,a+n+1);
	for(unsigned long long i=1;i<=n;i++){
		b[a[i]]++;
	}
	for(unsigned long long i=1;i<=n;i++)
		for(unsigned long long j=i+1;j<=n;j++){
			unsigned long long sum=a[i]+a[j];
			if(b[sum]>=2)
				ans+=b[sum]*(b[sum]-1)/2;
			ans%=1000000007;
		}
	cout<<ans;
	return 0;
}